Osteoarthritis (OA), the most prevalent form of arthritis, affects up to 15% of the adult population and is principally characterized by degeneration of the articular cartilage component of the joint, often with accompanying subchondral bone lesions. Understanding the mechanisms underlying the pathogenesis of OA is important for the rational development of disease modifying OA drugs (DMOADs). While most studies on OA have focused on the investigation of either the cartilage or the bone components of the articular joint, the osteochondral complex represents a more physiologically relevant target as the disease ultimately is a disorder of osteochondral integrity and function. In this application, we propose to construct an in vitro 3-dimensional microsystem that models the structure and biology of the osteochondral complex of the articular joint. Osteogenic and chondrogenic tissue components will be produced using adult human mesenchymal stem cells (MSCs) derived from bone marrow and adipose seeded within biomaterial scaffolds photostereolithographically fabricated with defined internal architecture. A 3D-printed, perfusion-ready container platform with dimensions to fit into a 96-well culture plate format is designed to house and maintain the osteochondral microsystem that has the following features: (1) an anatomic cartilage/bone biphasic structure with a functional interface; (2) all tissue components derived from a single adult mesenchymal stem cell source to eliminate possible age/tissue type incompatibility; (3) individual compartments to constitute separate microenvironment for the synovial and osseous components; (4) cell-seeded envelopes to represent synovium and endothelium; (5) accessible individual compartments that may be controlled and regulated via the introduction of bioactive agents or candidate effector cells, and tissue/medium sampling and compositional assays; (6) compatibility with the application of mechanical load and perturbation; and (7) imaging capability to allow for non-invasive functional monitoring. The robustness and physiological relevance of the osteochondral microsystem will be tested on the basis of: (1) structural integrity and potential connectivity of the separate synovial and osseous compartments; (2) maintenance of distinct cartilage and bone phenotypes and the development of a histologically distinct osteochondral junction or tidemark; (3) applicability and tissue responsiveness to mechanical loading; and (4) imaging and analytical capabilities. The consequences of mechanical injury, exposure to inflammatory cytokines, and compromised bone quality on degenerative changes in the cartilage component will be examined in the osteochondral microsystem as a first step towards its eventual application as an improved and high-throughput in vitro model for prediction of efficacy, safety, bioavailability, and toxicology outcomes for candidate DMOADs.